The intestinal epithelium presents the largest mucosal barrier between the internal host milieu and the external environment. Under physiological circumstances antigen trafficking occurs through three nonmutually exclusive pathways: transcellular, paracellular, and dendritic cell sampling within the intestinal lumen. When the delicate balance between controlled antigen trafficking and host immune response is lost, severe inflammation and overt clinical symptoms may develop. This negative outcome may be influenced by host genetic makeup, virulence traits of the intestinal pathogens, or the combination of both. The outcome of the interplay between host and intestinal microorganisms is influenced by the fact that the intestinal epithelium is extremely dynamic and exquisitely responsive to stimuli of innumerable variety and it is populated by a complex climax community of microbial partners, far more numerous than the cells of the intestine itself. In normal homeostasis, the gastrointestinal epithelial layer forms a tight, but selective barrier: microbes and most antigens are held at bay, but nutrients from the essential to the trivial are absorbed efficiently. Moreover, the tightness of the epithelial barrier is itself dynamic and depends on tight junctions (TJ) competency, though the mechanisms governing and affecting their permeability are poorly understood. What is becoming increasingly clear is that defects in epithelial permeability are associated with a large number of local and even systemic disorders. A common feature of enteric infections is their ability to increase epithelial permeability, an effect that initiates and promotes the host immune response. Mucosal permeability is also a factor in the delivery of mucosally introduced vaccines. With this project, we intend to capitalize on our combined expertise in mucosal biology, proteomics, genomics, microbiomics, biochemistry, and molecular biology to determine the role of alterations in mucosal barrier function in host-microbial interactions affecting antigen trafficking that lead to local and systemic immune responses to gastric and enteric pathogens. We will take full advantage of a very conducive environment that includes the Mucosal Biology Research Center, the Center for Vaccine Development and The Institute of Genomic Science, all thematically relevant to this proposal.